feat(push-panel): add a local page for editing push rules

[Yuna-Celisse]

Summary

• Add a PushPanel plugin that serves a loopback page for the live push rules: GitHub routes, calendar targets, repair digests, the Minecraft bridge groups, and the daily summary schedule.
• Saving updates the running plugin objects and writes config.json, so the next push uses the new rules. Empty token means the page does not listen. Model keys, bridge tokens, and other secrets are not shown or accepted.
• Code filters stay as they are: default-branch pushes, bot and dotfile skips, and the 60-minute / 5-minute calendar reminders.

Test plan

• dotnet test src/HuaJiBot.NET.UnitTest --filter FullyQualifiedName~PushPanelTest (5 tests: route update, rejected group, rejected bridge address, read of the other rules, HTTP 401 and save)
• After the image is on the stack, open http://127.0.0.1:8787/ through an SSH tunnel and confirm the current routes load